The OPs Javascript example is unnecessarily repetitive and complex. It shows plain Javascript in a bad light compared to jQuery when in fact it should be simpler and more concise. This is really not something jQuery should be used for.

document.getElementById('selectbox').value;

Was that so hard? With the element reference stored in a variable it would be as simple as this

selectbox.value;

And For comparison, the jQuery code

$('#selectbox').val();

IMO the plain Javascript is more readable, direct, and certainly more performant.

I would hardly consider this question academic as the example code is so trivial; it does not involve DOM traversal and has no cross browser compatibility issues, which are the main things jQuery was designed to address. So what the point is I'm not really sure...

This is incorrect. The OP's Javascript outputs the option tags' text, not its value. See jsfiddle.net/VhRBd/1. Your Javascript and jQuery versions are equivalent, but they're just not what was asked for.
–
Ingo BürkMay 23 '13 at 17:53